FROM FORAMS TO GLACIERS: TESTING THE SENSITIVITY OF BENTHIC FORAM MG/CA TO SEAWATER TEMPERATURE AND CHEMISTRY

Coupled measurements of foraminiferal δ¹⁸O and Mg/Ca are a promising new tool in unlocking history of past glaciations. Foram Mg/Ca has been shown to be an accurate proxy for paleo seawater temperature (T) and can be used with foram δ¹⁸O to calculate the oxygen isotopic composition of paleo-seawater (δw). This method has been applied on Quaternary timescales with success, but concerns about the secular variation of seawater Mg/Ca have clouded some interpretations of deeper time data. Currently, however, no experimentally-calibrated model explains how Mg/Ca of benthic forams calcite responds to variation of seawater T and Mg/Ca. Researchers have used several species of forams to study water chemistry and T, key parameters that record and predict environmental changes and paleotemperatures. Benthic foraminifera serve as a better indicator of bulk ocean properties, because they inhabit water masses less affected by cyclic variations in water properties. To this end, we have built a culture system for low-Mg calcite benthic forams. This system uses a series of tanks and refrigeration systems that were designed in consultation with aquaculture experts, engineers, and biologists. Each culture tank will be connected to a central filtration system, and will host a single species. If maintained, the cultures could be viable for years; it is constructed of common material (like PVC and plastic containers), requires minimal water changes due to large water to waste ratio, and all components are inexpensive and easy to replace. This colony will give access to a constant supply/variety of test subjects, which can then be subjected to different environmental conditions in individual cultures. From this, data can be correlated to deep-sea forams and create a single, accurate model for paleothermometry over deep time (e.g. the past hundred million years). With a robust model for the effects of seawater T and Mg/Ca on foram Mg/Ca, it will be possible to reduce uncertainties surrounding deep-time estimates of paleo seawater temperature and the history to Cenozoic continental glaciation: both basic inputs into reconstructing global climate change.